1. Field of the Invention
The present invention relates to adjustable steering columns for vehicles and, more particularly, to an adjustable steering column having a break-away lever.
2. Description of the Related Art
The use of adjustable steering columns in automobiles and other vehicles is well known. Oftentimes, such steering columns have a steering shaft that extends through a pair of telescoping steering jacket members. Typically, these steering columns can be repositioned by pivoting the steering column about a tilt axis and by adjusting the axial length of the steering column. A locking mechanism is provided and, in its locked configuration, secures the steering column in a selected tilt and axial position and, in its unlocked configuration, releases the steering column so that it may be repositioned. Many such locking mechanisms include an actuating lever that is manually operated by the driver of the vehicle to move the locking mechanism between its locked and its unlocked configurations.
Known adjustable steering columns also often include an energy absorption feature. If the operator of the vehicle impacts the steering wheel during a collision event, such features absorb part of the energy of the impact force as the steering column collapses to thereby reduce the peak impact forces that are imparted to the operator of the vehicle. Depending on the steering column design, it may be possible for the operator of the vehicle to impact the actuating lever of the tilt and axial locking mechanism in such a collision event. It is known to use a “break-away” actuating lever with such tilt and axial locking mechanisms to limit the impact forces that can be imparted by the actuating lever.
FIGS. 1-3 illustrate a break-away lever that can be used with locking mechanisms for adjustable steering columns. It is intended that the impact force required to break-away the lever arm illustrated in FIGS. 1-3 from the steering column fall within the range of between 450 and 600 Newtons.
FIG. 1 is a partial exploded view of an adjustable steering column assembly 10 that illustrates one of two sidewalls between which is positioned a pair of telescoping steering jacket members. A camming assembly 14 is installed adjacent the exterior of sidewall 12 and forms a part of the locking mechanism that is used to secure the steering column in a desired tilt and axial position in a manner well known in the art. Inner camming assembly member 16 is fixed adjacent sidewall 12 and includes an arcuate recess 18. Intermediate camming assembly member 20 is positioned between outer camming assembly member 22 and inner member 16. Three camming pins 23 are seated in bores in intermediate member 20.
A multi-piece locking bolt 24 extends through camming assembly 14, sidewall 12, the steering column and the opposite sidewall. Lever arm 26 is secured to outer member 22 in which the head of locking bolt 24 is seated. Outer member 22 includes a limit pin 28 that is seated in arcuate recess 18. The interaction of limit pin 28 and arcuate recess 18 limits the arc through which outer member 22 may be pivoted about the axis defined by locking bolt 24.
Lever arm 26 is secured to outer member 22 and pivotal motion of lever arm 26 pivots outer member 22. As lever arm 26 and outer member 22 are pivoted, pins 23 are seated and unseated from three depressions 25 in outer member 22. When pins 23 are seated in depressions 25, outer member 22 is positioned relatively close to inner member 16. When the pivotal motion of outer member 22 unseats pins 23 from depressions 25, outer member 22 and the head of bolt 24 seated therein are biased away from inner member 16.
When lever arm 26 is pivoted to its lowermost (unlocked) position, pins 23 are seated in depressions 25 and pivoting lever arm 26 to its uppermost (locked) position closest to the steering column assembly unseats pins 23 from depressions 25 biasing outer member 22 outwardly from inner member 16. When lever arm 26 is in its locked position and outer member 22 and the head of locking bolt 24 is biased away from inner member 16, the two sidewalls are biased together and secure the steering column in position. Movement of lever arm 26 to its unlocked position allows outer member 22 to move toward inner member 16 which thereby releases the steering column from its securement between the two sidewalls and permits the tilting and axial adjustment of the steering column. FIG. 2 illustrates one of the pins 23 in a seated condition within a depression 25 on outer member 22.
FIGS. 2 and 3 provide a more detailed view of lever arm 26 and its mounting to outer member 22. Outer member 22 is a metal body that can be formed by either casting or machining while lever arm 26 is formed by stamping a sheet metal material. The forward end of lever arm 26 has a grip 30 mounted thereon which can be grasped by the operator of the vehicle for moving lever arm 26 between its locked and unlocked positions. As best seen in FIG. 2, lever arm 26 is provided with injection holes 32 through which a plastic material 34 is injected. With reference to FIG. 3, plastic material 34 fills the spaces 33 between outer member 22 and lever arm 26 within the C-shaped portion of lever arm 26 in which outer member 22 is disposed. (Plastic material 34 has not been illustrated in FIG. 2.) This plastic material 34 secures outer member 22 and lever arm 26 together. If lever arm 26 is impacted by the operator of the vehicle as indicated by impact force arrow 36, the plastic material 34 securing outer member 22 and lever arm 26 will fail allowing lever arm 26 to become disengaged from outer member 22. The failure of the plastic material 34 required to allow lever arm 26 to be separated from outer member 22 requires at least the partial fracture of the plastic material, e.g., the severing of the sprues filling injection holes 32, and either the further fracture of the plastic material or the breaking of adhesive bonds between the plastic material and one or both of the lever arm 26 or outer member 22.
While providing a break-away lever, the lever illustrated in FIGS. 1-3 has several drawbacks. The injection molding process is labor intensive, and thus expensive, and the loads required to break-away the lever can be erratic due to the variations in the injection pressure, moisture and part variations. Moreover, the imposition of a plastic material between the lever arm and locking assembly requires that torsional and lateral loads imparted by the lever to the locking assembly be transferred through the injection molded plastic material. This undesirably reduces the stiffness of the lever arm as felt by the operator of the vehicle when using the lever under normal conditions to lock and unlock the steering column.